I had several aggregate checks like this:
grpsum('mygrp','srv.totalerrors','last','0')

After upgrade from 1.0.7 to 1.4.2 first i noticed my server was crashing instantly after start until I disabled all my grpsum items.

If i try to edit item it complains that syntax is incorrect because it doesn't like () in it. If i replace () with [] server doesn't crash anymore but item goes instantly into "unsupported" state (server doesn't crash anymore though).

so there are 2 problems most likely

1. UI does not accept () in key syntax for aggregate checks.
2. Server crashes for certain aggregate checks such as one listed above at the beginning of the message.

http://www.zabbix.com/forum/showthread.php?t=7564